Voice over IP (VOIP) is a technology that permits the delivery of voice communications over networks that implement the Internet Protocol (IP), such as the Internet. A VOIP network includes a plurality of client computers running software that supports VOIP. Voice connections can be created between client computers. Other devices, for example landline or mobile phones, can be connected to the VOIP network using a gateway. In addition, a mobile phone that runs VOIP software can be directly connected to a VOIP network.
Because more than one device, for example a landline and a mobile phone, may be for the same user, a user may want to transfer a telephone call received on one user device to another user device. In order to facilitate a telephone call transfer from one device to another device for the same user, a VOIP network may include one or more dedicated server computers, in some examples known as anchor servers, in which a telephone call is anchored for devices of the same user. An anchor server provides a fixed connection to a remote party in which a telephone call to the remote party can be switched from one user device to another use device.